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Scientists Detect Probable Genetic Cause of Some Parkinson's Disease

- Jan 28 2005

Two new studies strongly suggest that a mutation in a recently discovered gene is the most common genetic cause of Parkinson's disease identified to date. The discovery by an international research team provides fresh evidence that genetics may contribute to the development of some cases of Parkinson's disease. The findings could lead to the development of a genetic test to detect the mutation in individuals at risk. The research team includes investigators at the National Institute on Aging (NIA) and scientists supported by the National Institute of Neurological Disorders and Stroke (NINDS).

Parkinson's disease, which affects at least 500,000 Americans, is a progressive neurologic disorder that is caused by the degeneration of nerve cells in the portion of the brain that controls movement. Scientists have long suspected genetics plays a role in the onset of the disease. In these studies, the investigators found that a mutation in the gene LRRK2 appears to occur in at least one of every 60 people who have the disease. Overall, the mutation could be responsible for up to five percent of Parkinson's disease in people with a family history of the disorder and may account for one to two percent of cases in individuals who do not have a family history of the disease. The researchers found a mutation in one copy of the gene can lead to the disease. The findings were published online by Lancet at 6:30 PM ET on January 17, 2005.

"Among the forms of Parkinson's disease that are genetic in origin, this gene mutation causes more cases of Parkinson's disease than any other gene discovered to date," says Andrew Singleton, Ph.D., chief of the Molecular Genetics Unit in the NIA's Laboratory of Neurogenetics. "Knowing that this mutation is not only important in familial forms of disease, but in typical sporadic disease, where there is no strong family history, could lead to earlier detection of Parkinson's disease. Further study of how this gene works also might help scientists identify new treatments."

In addition to Dr. Singleton, the collaborative work was spearheaded by William C. Nichols, Ph.D., of Cincinnati Children's Hospital, Tatiana Foroud, Ph.D., of Indiana University Medical Center, Indianapolis, and Nicholas W. Wood, M.D., of the Institute of Neurology in London. The NIA and the NINDS are part of the National Institutes of Health (NIH) at the U.S. Department of Health and Human Services.

Singleton and his colleagues recently discovered LRRK2, a gene that encodes a protein named dardarin by the researchers from the Basque word dardara, which means tremor, a major symptom of Parkinson's disease. It was isolated on a region of chromosome 12 called PARK8 by investigators who studied five families with a history of Parkinson's disease who lived in the Basque region of Spain and in England.

In these new studies, the researchers sought to determine the prevalence of the genetic mutation in other families and individuals being studied by the Parkinson's Study Group with NINDS support. In an analysis of 358 families with a history of Parkinson's disease, for instance, the investigators found that 34 of the 767 people who had inherited the disease had at least one copy of the mutated gene. Similarly, the team detected one copy of the mutation in 8 of 482 people with Parkinson's disease, but who didn't report a family history of the disease. The Parkinson's Study Group is a non-profit, cooperative group of Parkinson's disease experts from 59 medical centers in the United States and Canada who are dedicated to improving treatment for people affected by Parkinson's disease.

"NINDS is pleased to have supported the collection of this large group of families and sibling pairs, which is proving to be an invaluable resource for these studies," says Diane Murphy, Ph.D., a program director at NINDS. "Because the prevalence of this mutation is five percent in families with a history of the disease and it is relatively common even among those without a family history, it's possible that detecting this mutation will help identify people at increased risk for Parkinson's disease."

Every new genetic finding that is published brings us one step closer to understanding the cause of Parkinsonís disease. The latest finding that a single genetic change in the gene LRRK2 may cause PD in up to five percent of people with Parkinsonís, who have a family history of PD, and one-to-two percent of people with PD who do not have a family history, is an exciting and important discovery. Although this finding implicates LRRK2 as one of the most important Parkinsonís disease genes discovered to date, the discovery still does not account for the cause of PD in the majority of people.

What is now becoming clear is that numerous genetic factors and environmental factors probably play a part in causing the disease. It is therefore even more crucial that research should focus on finding new genetic and environmental risk factors so that we gain the knowledge necessary to fight this disease.

For more information on Parkinsonís disease and genetics, please see Dr. Harrisís article, "Nature Versus Nurture: What Causes PD?" in the Fall 2004 issue of the PDF News & Review. You can request a copy by calling PDF at (800) 457-6676.